Optical sensors for position measurements

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Optical sensors for position measurements

Schroer, G. / Lutz, R. / Groegor, E.

Two sensors have been developed for autonomous rendezvous and docking manoeuvres in space in the range up to 100 m. The first is a proximity sensor, which is dedicated for distance and angle measurements. The sensor's equipment consists of three units: the position-sensitive detector, the illuminator and the common optics including a c.w. laser rangefinder. On the target side a corresponding reflector complements the necessary equipment to measure distance and angle deviation from boresight direction. The measured resolution of the sensor for a distance of 2 m is less than 2 mm and the angle resolution within a field of view of plus/minus 3 deg is less than 0.1 mrad. The use of at least three proximity sensor systems and a dedicated software enables position definition for six DOF (degrees of freedom) to be achieved. The actual operation wavelengths are between 790 and 850 nm. The second is a high-resolution CCD-camera in combination with a dedicated S/W processor, which is used for distances between 2 m and 100 m. On the target side, a three-dimensional symmetric pyramid reflector configuration is currently used. The camera processor transforms the actually depicted reflector configuration differences to the expected reflector configuration for boresight position into distance and position information for six DOF. This method can achieve faster update repetition rates (10 Hz) than a common pattern recognition technique. The camera is equipped with a 880 nm wavelength LED illuminator.